The present invention relates to service generator checking apparatus and a method in a telephone system operating in time frames each consisting of a plurality of time slots.
Pulse code modulated (PCM) digital signals in a telephone system enable a multiplicity of conversations to be transmitted over a two wire digitally multiplexed line commonly known as a T1 trunk line. A T1 line is multiplexed with other T1 lines to form what is known as a line group. The multiplexed PCM data from the line group is then applied to a time slot interchanger for switching the data from one time slot of a data group to another time slot of another line group.
Referring to the above-referenced patent application entitled "Integrated Message Timing System," there is employed therein a message accounting system with electronic solid state design which employs redundancy in all major subsystems where a single point failure could cause the system to go down. Faulty subsystems are automatically switched off line to provide minimum interruption to service.
The above-identified application includes line groups interfaced between T1 lines and time slot interchangers, thereby providing conversion between bipolar PCM signals on the T1 line and the internal system logic levels.
Referring to the above referenced application entitled "Service Generator For Generating A Plurality Of Tones," there is provided a service generator providing necessary tones such as dial tone and ring back tone used by the telephone system. The service generator is capable of generating and sending a selected tone to a selected one of the time slots in the telephone system. The tones are sent through the line groups to the trunk lines.
As previously mentioned, redundancy is employed in all major subsystems including the line group, where a single point failure could cause the system to go down. Primary and secondary subsystems of the system are provided to insure that any faulty subsystem may automatically be switched off line and the backup system simultaneously switched on line to provide minimum interruption to service.
The off line subsystem to be switched on line should be in fact ready for service, or otherwise switching a faulty subsystem on line would interrupt service and the entire system could go down.
In accordance with the above background, there is a need for service generator checking apparatus and a method to verify that an off line subsystem is at all times operational and ready for service.
In addition, is desirable that the service generator itself be checked at appropriate times to verify that any tones being transmitted are in the proper format.